You can also swap two numbers without using temp or temporary or third variable. In that case c program will be as shown :-

#include <stdio.h>

int main()

{

int a, b;

printf("Enter two integers to swap\n");

scanf("%d%d", &a, &b);

a = a + b;

b = a - b;

a = a - b;

printf("a = %d\nb = %d\n",a,b);

return 0;

}

To understand above logic simply choose a as 7 and b as 9 and then do what is written in program. You can choose any other combination of numbers as well. Sometimes it's a good way to understand a program.